Bottom Line:
To elucidate the pure impact of microgravity on small mammals despite uncontrolled factors that exist in the International Space Station, it is necessary to construct a 1 g environment in space.Accordingly, biological responses to hypergravity induced by a short-arm centrifuge were examined and compared with those induced by a long-arm centrifuge.Hypergravity induced a significant Fos expression in the central nervous system, a suppression of body mass growth, an acute and transient reduction in food intake, and impaired vestibulomotor coordination.

ABSTRACTTo elucidate the pure impact of microgravity on small mammals despite uncontrolled factors that exist in the International Space Station, it is necessary to construct a 1 g environment in space. The Japan Aerospace Exploration Agency has developed a novel mouse habitat cage unit that can be installed in the Cell Biology Experiment Facility in the Kibo module of the International Space Station. The Cell Biology Experiment Facility has a short-arm centrifuge to produce artificial 1 g gravity in space for mouse experiments. However, the gravitational gradient formed inside the rearing cage is larger when the radius of gyration is shorter; this may have some impact on mice. Accordingly, biological responses to hypergravity induced by a short-arm centrifuge were examined and compared with those induced by a long-arm centrifuge. Hypergravity induced a significant Fos expression in the central nervous system, a suppression of body mass growth, an acute and transient reduction in food intake, and impaired vestibulomotor coordination. There was no difference in these responses between mice raised in a short-arm centrifuge and those in a long-arm centrifuge. These results demonstrate the feasibility of using a short-arm centrifuge for mouse experiments.

pone.0133981.g006: A: Summarized data for daily measurements of body mass and food intake per 10 g of body mass during the 1-week acclimation period and the subsequent 4-week 1.4 g period. * P < 0.05 vs. Int-1g mice. B: duration for which the mice could maintain themselves on the rotarod before and after the 4-week 1.4 g load.The open bar (Pre) and filled bar (Post) represent data obtained before and just after the 1.4 g load, respectively. * P < 0.05 vs. Pre.

Mentions:
No mice died during the 1.4 g experiments. Fig 6A shows daily measurements of body mass and food intake during the 1-week acclimation period and the subsequent 4-week 1.4 g period. In the Int-1g mice, body mass tended to decrease during acclimation to the individual cage, reached a plateau on day 5–7, and then gradually increased from 22.2 ± 0.3 to 24.6 ± 0.3 g at the end of the 4-week experimental period. In both the Int-1.4g-S and the Int-1.4g-L mice, their body masses decreased at the onset of 1.4 g, reaching a nadir (20.0 ± 0.7 g in Int-1.4g-S and 20.4 ± 0.2 g in Int-1.4g-L) on day 2 or 3, and then gradually increased. However, the body masses in the Int-1.4g-S (23.1 ± 0.5 g) and the Int-1.4g-L (23.3 ± 0.1) did not catch up with those in the Int-1g at the end of the experimental period. There was a significant interaction between group and time [F(2,70) = 10.573, P < 0.001]. The body mass responses of the Int-1.4g-S and the Int-1.4g-L were significantly different from those of the Int-1g, but no difference was found between the Int-1.4g-S and the Int-1.4g-L (P = 0.942).

pone.0133981.g006: A: Summarized data for daily measurements of body mass and food intake per 10 g of body mass during the 1-week acclimation period and the subsequent 4-week 1.4 g period. * P < 0.05 vs. Int-1g mice. B: duration for which the mice could maintain themselves on the rotarod before and after the 4-week 1.4 g load.The open bar (Pre) and filled bar (Post) represent data obtained before and just after the 1.4 g load, respectively. * P < 0.05 vs. Pre.

Mentions:
No mice died during the 1.4 g experiments. Fig 6A shows daily measurements of body mass and food intake during the 1-week acclimation period and the subsequent 4-week 1.4 g period. In the Int-1g mice, body mass tended to decrease during acclimation to the individual cage, reached a plateau on day 5–7, and then gradually increased from 22.2 ± 0.3 to 24.6 ± 0.3 g at the end of the 4-week experimental period. In both the Int-1.4g-S and the Int-1.4g-L mice, their body masses decreased at the onset of 1.4 g, reaching a nadir (20.0 ± 0.7 g in Int-1.4g-S and 20.4 ± 0.2 g in Int-1.4g-L) on day 2 or 3, and then gradually increased. However, the body masses in the Int-1.4g-S (23.1 ± 0.5 g) and the Int-1.4g-L (23.3 ± 0.1) did not catch up with those in the Int-1g at the end of the experimental period. There was a significant interaction between group and time [F(2,70) = 10.573, P < 0.001]. The body mass responses of the Int-1.4g-S and the Int-1.4g-L were significantly different from those of the Int-1g, but no difference was found between the Int-1.4g-S and the Int-1.4g-L (P = 0.942).

Bottom Line:
To elucidate the pure impact of microgravity on small mammals despite uncontrolled factors that exist in the International Space Station, it is necessary to construct a 1 g environment in space.Accordingly, biological responses to hypergravity induced by a short-arm centrifuge were examined and compared with those induced by a long-arm centrifuge.Hypergravity induced a significant Fos expression in the central nervous system, a suppression of body mass growth, an acute and transient reduction in food intake, and impaired vestibulomotor coordination.

ABSTRACTTo elucidate the pure impact of microgravity on small mammals despite uncontrolled factors that exist in the International Space Station, it is necessary to construct a 1 g environment in space. The Japan Aerospace Exploration Agency has developed a novel mouse habitat cage unit that can be installed in the Cell Biology Experiment Facility in the Kibo module of the International Space Station. The Cell Biology Experiment Facility has a short-arm centrifuge to produce artificial 1 g gravity in space for mouse experiments. However, the gravitational gradient formed inside the rearing cage is larger when the radius of gyration is shorter; this may have some impact on mice. Accordingly, biological responses to hypergravity induced by a short-arm centrifuge were examined and compared with those induced by a long-arm centrifuge. Hypergravity induced a significant Fos expression in the central nervous system, a suppression of body mass growth, an acute and transient reduction in food intake, and impaired vestibulomotor coordination. There was no difference in these responses between mice raised in a short-arm centrifuge and those in a long-arm centrifuge. These results demonstrate the feasibility of using a short-arm centrifuge for mouse experiments.